276 



ORDER XI. SIPHONOSTOMA. 



887. We next pass to the group of Suctorial Entomostraca, 

 in which the mouth, instead of being furnished with mandibles 

 and maxillae adapted for the division of solid aliment, is prolonged 

 into a beak, and can only receive liquid substances. Still among 

 the Crustacea, as in Insects, the parts which compose the Mandi- 

 bulate mouth of the preceding Orders, may be recognised in the 

 Haustellate or Suctorial mouth of those we have now to consider. 

 The proboscis is formed by a prolongation of the upper and lower 

 lip ; and it is generally accompanied by a pair of long append- 

 ages, which evidently correspond with the mandibles of the pre- 

 ceding Orders, and which serve to make the punctures into which 

 the proboscis is inserted. Other appendages, found at its base, 

 are the representatives of the maxillae and feet-jaws of the Man- 

 dibulate Orders ; and these are frequently developed as hooks, by 

 which the animal attaches itself to its prey. Many of the Suc- 

 torial Crustacea bear a strong resemblance in their general form 

 to the Cyclops and other Copepoda. The body is usually divided, 

 at its anterior part at least, into distinct segments ; and there are 

 generally four pairs of legs, each furnished at its extremity with 

 two oar-like expansions. The resemblance is often strongest in 

 the early stages of development ; the young Lerncea, for example 

 (Fig. 612), being scarcely distinguishable from the young Cyclops 

 (Fig. 606). But in their advance towards maturity, the Suctorial 

 Crustacea frequently undergo the most extraordinary changes ; 

 so that, if we were to attend to their adult forms alone, we should 

 be tempted to exclude them from the class altogether, in so small 

 a degree do they present its distinguishing characters. 



888. The Crustacea of the Order SIPHONOSTOMA are all pa- 

 rasitic upon Fishes, aquatic Batrachia, &c. ; and many of them 

 are known under the name of Fish-lice. Their general charac- 



